The treatment of surfaces of fillers to improve filler/matrix bonding in thermoplastic and thermoset composites and in filled rubber systems is known. Thus in U.S. Pat. Nos. 4,514,231 and 4,704,414 the treatment of siliceous fillers with polysulfidic silylethers, in particular bis-(triethoxysilyl-propyl) tetrasulfide, is described. According to DE 2 141 159 and 2 255 577, the surface modification of untreated fillers can be performed in situ by adding polysulfidic silylether to a mixture of the corresponding rubbers and untreated filler. The disadvantage of using polysulfidic silylethers to improve the filler/matrix bonding is the costly method of preparation of the polysulfidic silylethers and the associated high cost of raw materials. U.S. Pat. Nos. 2,736,669 and 2,801,185 describe processes for rendering silica hydrophobic in which silicas are treated with alcohols. The silicas treated in this way, however, do not exhibit an improved reinforcing effect in a rubber matrix.
EP 0 631 982 describes a special method for preparing silica aggregates and their use for reinforcing elastomers. As is also specified in EP 0 631 982, the silica aggregates which are obtained may be provided with additional functional groups in a subsequent reaction. A number of chemical compounds with functional groups is used for treating the silica aggregates obtained in order to introduce a variety of functional groups. The silicon-free compounds for treating silica aggregates, listed in particular in column 8 of the European patent application mentioned above, do not produce sufficient improvement in the reinforcing fillers with regard to the physical properties of the rubber mixtures prepared therefrom, in particular when they are intended for the preparation of highly reinforced, abrasion-resistant moulded items.